Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Richard Pažout

Lillianite homologues from Kutná Hora ore district, Czech Republic: a case of large-scale Sb for Bi substitution

Journal of Geosciences, volume 62 (2017), issue 1, 37 - 57

DOI: http://doi.org/10.3190/jgeosci.235

Numerous complex Pb-Bi-Sb-Ag sulphosalt minerals belonging to the lillianite homologous series previously unknown in Czech Republic, including a new mineral species, have been identified in samples from hydrothermal vein mineralization of the Kutná Hora Ag-Pb-Zn ore district, central Bohemia, Czech Republic. Identified lillianite homologues include both Bi members (minerals of the lillianite branch) and Sb members (andorite branch) and show an extensive Sb for Bi substitution. Nine distinct compositional groups were identified among Bi members, corresponding to: N = 4 (gustavite, terrywallaceite, staročeskéite - recently approved IMA No. 2016-101), N = 5.5 (vikingite), N = 6 (treasurite), N = 7 (eskimoite and (Ag, Bi)-rich heyrovskýite), N = 8 (erzwiesite) and schirmerite (Type 2). Single-crystal XRD measurement of Bi members with N = 4 revealed a new mineral, staročeskéite. Unlike gustavite and terrywallaceite, which are monoclinic, staročeskéite is orthorhombic with a = 4.2539(8), b = 13.3094(8), c = 19.625(1) Å, and the ideal formula is Ag_0.70Pb_1.60(Bi_1.35Sb_1.35)_Σ2.70S₆, corresponding to N_chem = 4, Bi/(Bi + Sb) = 0.50 and substitution percentage L% = 70. Among Sb members, minerals with N = 4 (andorite series) and N = 5.0-5.5 were found. Relations between substitution percentage, chemical N and Sb content have been observed. The description of the new occurrence of Bi sulphosalts, including Sb-rich varieties and a continuous transition from Bi-dominant to Sb-dominant phases with N = 4 provides new information on compositional limits in natural sulphosalts. Comparable range of the Bi³⁺ ↔ Sb³⁺substitution in lillianite homologues with N = 4 has not been observed before.